CLHS: Function MAPHASH

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Function MAPHASH

Syntax:

maphash function hash-table => nil

Arguments and Values:

function---a designator for a function of two arguments, the key and the value.

hash-table---a hash table.

Description:

Iterates over all entries in the hash-table. For each entry, the function is called with two arguments--the key and the value of that entry.

The consequences are unspecified if any attempt is made to add or remove an entry from the hash-table while a maphash is in progress, with two exceptions: the function can use can use setf of gethash to change the value part of the entry currently being processed, or it can use remhash to remove that entry.

Examples:

     (setq table (make-hash-table)) =>  #<HASH-TABLE EQL 0/120 32304110>
     (dotimes (i 10) (setf (gethash i table) i)) =>  NIL
     (let ((sum-of-squares 0))
        (maphash #'(lambda (key val)
                     (let ((square (* val val)))
                       (incf sum-of-squares square)
                       (setf (gethash key table) square)))
                 table)
        sum-of-squares) =>  285
     (hash-table-count table) =>  10
     (maphash #'(lambda (key val)
                   (when (oddp val) (remhash key table)))
               table) =>  NIL
     (hash-table-count table) =>  5
     (maphash #'(lambda (k v) (print (list k v))) table)
    (0 0)
    (8 64)
    (2 4)
    (6 36)
    (4 16)
    =>  NIL

Side Effects:

None, other than any which might be done by the function.

Affected By: None.

Exceptional Situations: None.

See Also:

loop, with-hash-table-iterator, Section 3.6 (Traversal Rules and Side Effects)

Notes: None.

The following X3J13 cleanup issue, not part of the specification, applies to this section:

- MAPPING-DESTRUCTIVE-INTERACTION:EXPLICITLY-VAGUE

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